Formation coring is required for the detailed study and analysis of a vertical section of reservoir or other rock layers. To retrieve the core as intact as possible, it is cut from the rock by an annular core bit. The central column of rock passes through the centre of the coring bit and, as the bit cuts deeper, is received by a hollow cylindrical Core Barrel above the coring bit, where it is protected by a series of rubber baffles. When the bit has cut deep enough to fill the core barrel, it is withdrawn from the hole and the core is removed for study. By doing this the actual sequence of rock strata can be readily identified.
To as greatest extent as possible, core samples are taken in an undamaged, physically unaltered state. The formation material may be solid rock, friable rock, conglomerates, unconsolidated sands, coal shales, gumbos, or clays.
A typical coring tool in use today can be seen in WO 2007/027683. In this coring tool only relatively small core samples can be obtained and also only one core can be acquired before having to retrieve the tool to the surface for analysis.
Other examples of coring tools can be found in US 2007/0215349, U.S. Pat. Nos. 4,714,119 and 5,667,025.